1. Field of the Invention
The present invention relates to an image forming method and apparatus, and more particularly to an image forming method and apparatus for creating raster data on the basis of image data written in a page description language, and forming an image on the basis of the created raster data.
2. Description of the Related Art
Typically, documents and so on created on a PC (personal computer) or the like are transmitted to an image forming apparatus such as a printer in a page description language. Raster data based on the page description language are then created in the image forming apparatus, whereupon image processing such as screen processing or the like is implemented on the created raster data. The document is then printed onto paper or the like and output.
With recent application software, it has become possible to apply pattern fill processing such as halftone dot meshing or translucence to created documents. In certain cases, however, the parts to which such pattern fill processing has been applied, as well as small characters, thin lines, and so on disappear due to interference with the screen used in the screen processing in the image forming apparatus.
For example, when 25% halftone dot meshing processing is implemented on a filled region such as that shown in FIG. 13A, raster data such as those shown in FIG. 13B are created. When screen processing using a 50% screen, such as that shown in FIG. 13C, is applied thereto, the processing result is as shown in FIG. 13D, where the halftone dot meshing pattern has altered greatly. Note that in FIGS. 13A to 13D, the diagonally shaded parts are rendered parts, and the pattern in FIG. 13D, which shows the result of the screen processing, is the product of the patterns shown in FIGS. 13B and 13C (AND processing).
When screen processing using a 50% screen such as that shown in FIG. 14B is implemented on a thin line such as that shown in FIG. 14A, the processing result is as shown in FIG. 14C, where the original thin line has become a dotted line with wide intervals. Note that in FIGS. 14A to 14C, the diagonally shaded parts are rendered parts, and the pattern shown in FIG. 14C, which shows the result of the screen processing, is the product of the patterns shown in FIGS. 14A and 14B (AND processing).
Likewise, when screen processing using a 50% screen such as that shown in FIG. 15B is implemented on a character such as that shown in FIG. 15A, the processing result is as shown in FIG. 15C, where many parts of the original character have been deleted. Note that in FIGS. 15A to 15C, the diagonally shaded parts are rendered parts, and the pattern shown in FIG. 15C, which shows the result of the screen processing, is the product of the patterns shown in FIGS. 15A and 15B (AND processing).
Examples of techniques for preventing deterioration of the image quality caused by such interference with the screen include amending the phenomenon whereby a pattern disappears by adding processing such as pattern modification when a pattern produced by a pattern fill command seems likely to disappear due to interference with the screen or the like (for example, Japanese Patent Application Laid-Open No. 2003-168124), performing processing when an isolated dot is detected to emphasize the dot and its periphery (for example, Japanese Patent Application Laid-Open No. 2001-45299), and so on.
However, in both the technique described in Japanese Patent Application Laid-Open No. 2003-168124 and the technique described in Japanese Patent Application Laid-Open No. 2001-45299, patterns are made more distinguishable by adding modifications to the original pattern, and hence time is required to detect the pattern and apply modification processing thereto.
Moreover, although the processing time can be shortened by implementing these processes using hardware, large costs are involved in constructing the hardware.